Methods and apparatus for mitigating fading in a broadband access system using drone/uav platforms

ABSTRACT

Systems and methods for mitigating the effects of atmospheric conditions such as rain, fog, cloud in a broadband access system using drone/UAVs. In one embodiment, terminal and drone radio and transmission medium fixture sub-systems comprise multiple transmission media. In one embodiment, in response to changes in atmospheric conditions the drone radio sub-system switches transmission medium to reduce the effects of atmospheric conditions. In another embodiment, the terminal and drone radio sub-systems equalize the data rates among terminals in response to changes in atmospheric conditions observed by different terminals. In another embodiment, the drone radio sub-system adjusts the transmit power on the downlink to different terminal according to fading due to atmospheric conditions on each link.

PRIORITY

This application claims priority to co-owned, co-pending U.S. PatentProvisional Application Ser. No. 61/981,128, filed on Apr. 17, 2014, andentitled “METHODS AND APPARATUS FOR MITIGATING FADING IN A BROADBANDACCESS SYSTEM USING DRONE/UAV PLATFORMS”, the foregoing beingincorporated by reference herein in its entirety.

RELATED APPLICATIONS

The application is related to co-owned, co-pending U.S. patentapplication Ser. No. 14/222,497, and entitled “BROADBAND ACCESS TOMOBILE PLATFORMS USING DRONE/UAV”, filed on Mar. 21, 2014, and co-owned,co-pending U.S. patent application Ser. No. 14/223,705 entitled“BROADBAND ACCESS SYSTEM VIA DRONE/UAV PLATFORMS”, filed on Mar. 24,2014, each of the foregoing incorporated by reference herein in itsentirety.

COPYRIGHT

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent files or records, but otherwise reserves all copyrightrights whatsoever.

BACKGROUND

1. Technological Field

The present disclosure describes, among other things, aspects of asystem for broadband internet access using drones as a platform to relayinternet traffic among different types of terminals.

2. Description of Related Technology

As internet traffic has increased, new technologies are needed todeliver broadband access to homes and enterprises at lower cost and toplaces that are not yet covered. Examples of current broadband deliverysystems include terrestrial wired networks such as DSL (DigitalSubscriber Line) on twisted pair, fiber delivery systems such as FiOS(Fiber Optic Service), and geo-stationary satellite systems. The currentbroadband access systems have a number of short comings. One issue islack of service in remote and/or lightly populated areas. Geo-stationarysatellites do provide service in remote areas of the developed worldsuch as the United States. Poorer areas of the world, however, lackadequate satellite capacity.

A notable reason satellite capacity has not been adequately provided inpoor regions of the world is the relatively high cost of satellitesystems. Due to adverse atmospheric effects in satellite orbits,satellite hardware must be space qualified and is costly. Launchvehicles to put the satellites in orbit are also costly. Moreover, dueto the launch risk and the high cost of satellites, there may besignificant insurance costs for the satellite and the launch. Therefore,broadband satellite systems and services are relatively costly anddifficult to justify in poor regions of the world. It is also costly todeploy terrestrial systems such as fiber or microwave links in lightlypopulated regions. The small density of subscribers does not justify thedeployment cost.

SUMMARY

The present disclosure describes, inter alia, systems and methods forbroadband access to homes, enterprises, and mobile platforms (such asairplanes and vehicles) using a network of drones.

In a first aspect, a drone is disclosed. In one embodiment, the drone isconfigured to provide broadband access to one or more terminals, andincludes: at least one transmission medium fixture comprising at leastone transmission medium configured to provide coverage to one or moreterminals; at least one radio sub-system configured to demodulate anddecode one or more first signals received from the one or moreterminals, and modulate and transmit one or more second signals to theone or more terminals; and a drone switching sub-system configured toswitch data received at the drone to another receiving unit of the oneor more terminals and/or the one or more drones.

In one variant, the one or more terminals comprise one or moreground-based mobile terminals. The drone radio sub-system is furtherconfigured to determine an amount of transmission resources to beallocated to one or more downlinks of the different ones of the one ormore ground-based mobile terminals to equalize a data rate among thedifferent ones of the one or more ground-based mobile terminalsaccording to a fairness criterion. A scheduler is also included, thescheduler configured to schedule the determined amount of transmissionresources to the downlink of the different ones of the one or moreground-based mobile terminals.

In another aspect, a method of providing broadband access using aplurality of drones is disclosed. In one embodiment, the methodincludes: measuring a signal quality metric; comparing the measuredsignal quality metric for one or more terminals of a plurality ofterminals versus one or more threshold values; and determining if thesignal quality metric of the one or more terminals has degraded due toone or more atmospheric conditions.

In one variant, the method further includes determining a number oftransmission resources that an uplink and downlink to the one or moreterminals needs in order to equalize the throughput to different ones ofthe plurality terminals according to a specified fairness criterion. Inanother variant, a scheduler is informed of the allocated number oftransmission resources for each terminal link; and a message is sent toone or more terminals comprising respective uplink transmission resourceallocations.

In another aspect, a mobile terminal is disclosed. In one embodiment,the terminal includes a mobile terminal radio sub-system comprising atleast one transmission medium fixture configured for use with at leasttwo transmission mediums. In one variant, the mobile terminal radiosub-system is configured to: demodulate and decode one or more firstsignals received on at least one transmission medium of the at least twotransmission mediums from at least one of one or more drones; modulateand transmit the one or more first signals on the at least onetransmission medium to the at least one of the one or more drones; andresponsive to a switch instruction, the at least one transmission mediumfixture switches to a different transmission medium of the at least twotransmission mediums.

This disclosure describes systems and methods for mitigating rain, fog,cloud and other atmospheric effects for a drone based broadband accesssystem to homes, enterprises, and mobile platforms. The system comprisesone or more drones, each drone comprising at least one transmissionmedium fixture supporting at least one radio frequency or free spaceoptics transmission medium configured to provide coverage to one or moreground/mobile terminals. Each drone comprises at least one radiosub-system configured to demodulate and decode one or more first signalsreceived from the one or more ground/mobile terminals on at least onetransmission medium. The drone radio sub-system is further configured tomodulate and transmit one or more second signals to the one or moreground/mobile terminals on at least one transmission medium. Dronecommunications system further comprises a switching sub-systemconfigured to switch data received at the drone to another receivingunit. Each ground/mobile terminal comprises systems and methods todemodulate and decode the one or more second signals received on atleast one transmission medium from at least one of the one or moredrones corresponding thereto; and to modulate and transmit the one ormore first signals on at least one transmission medium to the at leastone of the one or more drones.

One aspect of the disclosure comprises systems and methods for: theground/mobile terminal radio sub-system to measure changes in receiveddownlink signal quality due to rain, fog, cloud and other atmosphericconditions, and to send the measured signal quality to the drone radiosub-system; the drone radio sub-system to determine the amount of timethat must be allocated to the downlinks of the different ground/mobileterminals to equalize the data rate among different terminals accordingto some fairness criterion; and the scheduler at the drone processor toschedule the determined number of time slots or bandwidth to thedownlink of different ground/mobile terminals.

Another aspect of the disclosure comprises: a drone radio sub-system todetermine changes on the uplink signal quality received from differentground/mobile terminals due to rain, fog, cloud and other atmosphericconditions; the drone radio sub-system to determine the amount of timethat must be allocated to the uplink of the different ground/mobileterminals to equalize the data rate among different terminals accordingto some fairness criterion; and the scheduler at the drone processor toschedule the determined number of time slots or bandwidth to the uplinkof different ground/mobile terminals.

Another aspect of the disclosure comprises systems and methods for theground/mobile terminal radio sub-system to measure changes in receiveddownlink signal quality due to rain, fog, cloud and other atmosphericconditions, and to send the measured signal quality to the drone radiosub-system; the drone radio sub-system to determine whether to switch toa different transmission medium on the downlink with less fading fromatmospheric conditions, and to send the information on the new mediumand the time to switch to the new downlink medium to the ground/mobileterminal; the drone radio sub-system to switch to the new medium on thedownlink at the specified time; and a ground/mobile terminal to switchto the new medium on the downlink at the specified time.

The system further comprises systems and methods for: the drone radiosub-system to measure changes in received uplink signal quality due torain, fog, cloud and other atmospheric conditions; the drone radiosub-system to determine whether to switch to a different transmissionmedium on the uplink with less fading due to atmospheric conditions, andto send the information on the new medium and the time to switch to thenew uplink medium to the ground/mobile terminal; the drone radiosub-system to switch to the new medium on the uplink at the specifiedtime; and the ground/mobile terminal to switch to the new medium on theuplink at the specified time.

Another aspect of the disclosure comprises systems and methods for: theground/mobile terminal radio sub-system to measure changes in receiveddownlink signal quality due to rain, fog, cloud and other atmosphericconditions, and to send the measured signal quality to the drone radiosub-system; the drone radio sub-system to determine changes in theamount of power allocated on the downlink to each ground/mobile terminalto equalize the data rate among different terminals according to somefairness criterion; and the drone radio sub-system to adjust the powerallocated to downlink of each ground/mobile terminal.

The TX unit of the drone radio sub-system comprises systems and methodsfor: encoding each terminal's data and mapping the coded bits ontoconstellation symbols; scaling the coded symbols from each terminaldestined to different antenna elements to form a beam toward theterminal; summing the scaled coded symbols from different terminalsdestined to the same antenna aperture to form multiple beams, one towardeach terminal; amplifying and up-converting the summed signal to theappropriate frequency band; and transmitting the resulting signalthrough the corresponding antenna aperture. In another aspect of thedisclosure, the drone TX unit comprises systems and methods to choosethe scaling for coded symbols for each terminal to adjust the power sentto that terminal on the downlink.

These and other aspects shall become apparent when considered in lightof the disclosure provided herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following figures, similar components are identified using thesame reference label. Multiple instances of the same component in afigure are distinguished by inserting a dash after the reference labeland adding a second reference label.

FIG. 1 is an exemplary block diagram of a drone/Unmanned Aerial Vehicle(UAV) based broadband access to internet system.

FIG. 2A-2B are block diagrams of exemplary drone and ground/mobileterminal radio sub-systems.

FIG. 3 is an exemplary diagram of drone based broadband access systemusing multiple transmission media to provide coverage to an area.

FIG. 4 is a flow chart illustrating an exemplary process to adjust oneor more data rates on the links between terminals and the drone inresponse to rain or other atmospheric conditions.

FIG. 5 is a flow chart of an exemplary process to switch a transmissionmedium between a drone and a terminal to mitigate fading due to e.g.,atmospheric conditions such as rain, fog, and/or clouds.

FIG. 6 is a block diagram of an exemplary apparatus configured tocontrol transmission power on one or more downlinks to differentterminals and further configured to form beams toward the one or moredifferent terminals.

FIG. 7 is a flow chart of an exemplary process to adjust powertransmitted on one or more downlinks to one or more different terminalsin response to changes in atmospheric conditions such as, e.g., rain,fog, and/or clouds.

All Figures © Copyright 2014 Ubiqomm, LLC All rights reserved.

DETAILED DESCRIPTION

Reference is now made to the drawings, wherein like numerals refer tolike parts throughout.

In view of the challenges and hurdles in both expense and access toremote, poor or otherwise underserved regions, there exists a need forimproved broadband access. Accordingly, a system that has much lowerhardware cost, has much lower launch/deployment cost, and is more easilyscalable is needed.

Until recently drones, also known as Unmanned Aerial Vehicles (UAVs),have been extensively used by military, as well as for some scientificapplications such as weather information gathering. Commercialapplications of drones/UAVs include package delivery systems, videogathering systems, and communications systems. This disclosure describesaspects of a communications system design that are optimized for usingdrones/UAVs as the communications platform. Since drones/UAVs have thecapability to fly at much lower altitudes than satellites do, such dronesystems have an exemplary benefit of not needing the expensive spacequalification of the satellite systems. Furthermore, drones/UAVs also donot need the expensive launch systems of satellites. Since the drone/UAVhardware cost is relatively small compared to satellites, and there isless of a launch risk, then there is a reduced need for additionalinsurance costs. Principles of the present disclosure therefore providehigh capacity drone/UAV based broadband communication systems. As such,the relatively low cost of the drone/UAV hardware and operation cost,and its high capacity result in a low cost broadband delivery system.

Another exemplary advantage of a drone/UAV system configured accordingto the present disclosure over satellite systems is the lowcommunication signal delay achievable by the drone/UAV systems. Forinstance, geo-stationary satellites typically have a round tripcommunication signal delay from ground to the satellite and back toground of about 0.5 seconds which significantly impacts the quality ofservices that require low round trip delays. Even high altitudedrones/UAVs (e.g., altitudes of 25 kilometers), would typically have around trip communication signal delay of about 2 milliseconds toterminals on the ground for distances up to 300 kilometers from thedrone. Accordingly, the low delay of drone/UAV based system of thepresent disclosure may enable similar real time quality as compared toterrestrial broadband access systems.

Another exemplary advantage of drones (configured according to thepresent disclosure) is that the drones may be deployed one at a time inareas with radiuses of 300 km or less and immediately provide servicewithin the drone's footprint. In contrast, satellite systems may need tocover a wide area before service may be provided (such as a large partof the CONUS (CONtinental US) in the case of geo-satellite systems, ormost of the earth in the case of LEO (Low Earth Orbit) satellitesystems). Therefore, drone based systems offer improved scalability whencompared to satellite systems, as a network provider can send one droneand start service in its footprint, test the market acceptance of theservice, and then send more drones in areas that need service.Furthermore, a network provider could deploy the drones in only areas ofthe country where there is a high demand for the service. In theremainder of this disclosure we use the term drone to refer to bothdrones and UAVs. In addition, it should be noted that principles of thepresent disclosure may be equally applied to other types of aerialvehicles. For example, blimps or balloons may be implementedalternatively, or in addition to, the drones as discussed herein, toprovide the broadband access system. Additionally, while the disclosedembodiments are described with respect to UAVs, it should be appreciatedby those of ordinary skill in the related arts that drones are by nomeans limited to aerial operation; drones may include watercraft,land-based vehicles, submersibles, and even spacecraft variants, suchimplementations being within the skill of an ordinary artisan, given thecontents of the present disclosure.

FIG. 1 illustrates one exemplary drone 110 configured according to thepresent disclosure. In one embodiment, each drone 110 has a drone radiosub-system 112 and at least one drone transmission medium fixture 114.The physical medium used to transmit the information may beelectromagnetic waves (e.g., radio) in different frequency bands or FreeSpace Optics (FSO). The term “transmission medium aperture” refers to anantenna aperture when considering electromagnetic waves, and refers toan optical lens when considering FSO. Therefore, the aperture of thetransmission medium fixture may be an antenna when using electromagneticwaves, or an optical aperture when using FSO. As shown in FIG. 2A, thedrone radio sub-system 112 includes four (4) sub-systems: the receiver318 that demodulates and decodes the signal received from an aperture ofthe transmission medium fixture 114; the transmitter sub-system 316 thatmodulates the data received from processor 314 and sends the resultingsignal through an aperture of the transmission medium fixture 114; theprocessor sub-system 314 that carries out functions such as configuringthe receiver 318 and transmitter 316 sub-systems, processing the datareceived from the receiver 318 sub-system, determining the data to betransmitted through the transmitter sub-system 316, as well ascontrolling the transmission medium fixture 114; and the memorysub-system 312 that contains program code and configuration, and systemparameter information that are accessed by the processor 318.

As shown in FIG. 2A, the radio sub-system transmitter 316 and receiver318 sub-systems support multiple frequency bands, F₁ . . . F_(n), aswell as FSO, and each sub-system comprises multiple TX and RX unitscorresponding to each supported frequency band F₁ . . . F_(n) or FSO. Aswill be discussed below, the specific frequency band, F₁ . . . F_(n), orFSO, that is used for communication to a specific Ground Terminal (GT)depends on the relative distance of the GT to the drone, as well as theatmospheric conditions at a given time. As used herein, a “groundterminal” may refer to a fixed terminal or a terminal on a mobileplatform such as a vehicle or an aircraft.

In one embodiment, a mechanism configured to connect the appropriatetransmitter and receiver frequency or FSO units to the processor isdisclosed. In one implementation, the radio sub-system 112 comprises aswitching sub-system 315 that switches the data from processor 314 tothe appropriate radio transmitter TX unit to modulate the data using theappropriate medium and to transmit the modulated signal through thecorresponding medium aperture. Similarly, a switching sub-system 315switches the data from the appropriate RX units of the receiversub-system 318 to the processor sub-system 314. The transmission mediumfixture 114 as shown in FIG. 2A includes a number of aperturessupporting frequency bands F1 to Fn and FSO. The TX and RX units of thetransmitter and receiver sub-systems are connected to the aperturecorresponding to the same frequency band or FSO.

Depending on the altitude of the drone 110, each drone 110 may cover anarea on the ground with a radius of tens of kilometers to hundreds ofkilometers or more. In one exemplary embodiment, drones 110 areconfigured to communicate with at least three kinds of ground terminals:one type of terminal is the Ground Terminal (GT) 120 (see FIG. 1), suchas terminals at home or enterprises to provide internet connectivity toa home or enterprise; a second type of terminal is installed on mobileplatforms such as vehicles or airplanes; a third type is what isreferred to as the internet Gateway (GTW) 130 which is connected to theinternet. GTs 120 transmit and receive data from the internet using thedrone network as an intermediary connection to network infrastructure.The drone's 110 radio sub-system 316 aggregates traffic received fromthe GTs 120 and may aggregate traffic received from multiple GTs 120 andsend the aggregated data to the internet via one of the GTWs 130.Therefore, in one embodiment, the GTWs 130 provide higher data ratesfrom/to drones than the data rates provided from the GTs 120. In theseembodiments, the gain of the GTW medium aperture sub-system is largerthan that of the GT 120, and the GTW 130 transmitter transmits at ahigher power than the GTs 120.

As shown in FIG. 2A, drone 110 further comprises a drone switchingsub-system 116. The switching sub-system 116 may route data receivedfrom one GT 120 to another GT 120 in the footprint of the drone, or fromone GT 120 to a GTW 130 which is in turn connected to the internet 136.

As shown in FIG. 2B, in one embodiment, the GT 120 is configured withtwo main sub-systems, a ground/mobile terminal radio sub-system 122, anda ground/mobile terminal transmission medium fixture 124. The GT radiosub-system 122 comprises four (4) sub-systems: the receiver 418 thatdemodulates and decodes the signal from drone medium aperture sub-system124 the transmitter sub-system 416 modulates the data and sends theresulting signal through an aperture of the transmission medium fixture124; the processor sub-system 414 is configured to execute software toperform various functions (such as configuring the receiver 418 andtransmitter 416 sub-systems, processing the data received from thereceiver sub-system 418, determining the data to be transmitted throughthe transmitter sub-system 416, as well as controlling the transmissionmedium fixture 124, etc.); and the memory sub-system 412 containsprogram code and configuration data, and system parameters informationthat are accessed by the processor 414. The switching sub-system 415connects the processor to the appropriate transmitter or receiver unitsof the transmitter 416 and receiver 418 sub-systems.

The link between the drones and the GTs 120 may operate in differentparts of the spectrum, F₁ . . . F_(n), or FSO. Since different parts ofthe spectrum are susceptible to atmospheric effects to differentdegrees, the range of the signal from the drone 110 to the groundterminals will depend on the particular frequency band being used.Frequencies above 10 GHz may suffer higher losses from rain fade thanfrequencies below 10 GHz; generally, higher frequencies incur higherfades. Frequencies above 10 GHz may also incur attenuation due toatmospheric gases such as oxygen and carbon dioxide (CO₂), as well aswater vapor. Optical signals suffer primarily from fog and clouds.

In one embodiment of the present disclosure, a mechanism that detectsand mitigates the effects of atmospheric losses is disclosed. In onevariant, the disclosed mechanisms also optimize trade-offs betweenfrequencies and ranges (e.g., higher frequencies have lower ranges).Specifically, different RF frequencies and optical links have differentranges, therefore the disclosed apparatus efficiently creates a widecoverage area using the different available frequency and optical bands.

FIG. 3 shows an exemplary embodiment where two frequency bands F₁ and F₂and FSO are used by the drone 110 and the GTs 120. The coverage area inthe footprint of the drone 110 is divided into a number of rings. Theinnermost ring that is served by all frequency bands as well as FSO hasthe smallest range. The next two rings shown in FIG. 3 may be too farfor FSO to reliably reach. As shown in FIG. 3, frequency band F1 has thelargest coverage ring. In one embodiment, F₁ has a lower frequency thanF₂; alternatively, the frequency band F₁ may be configured with a higherEIRP (Effective Isotopic Radiated Power) than F₂. GTs 120 in theoutermost ring of the coverage area would be served using the F₁frequency band, GTs 120 in the ring in the middle would be served usingeither F₁ or F₂ spectrum, and GTs 120 that are in the innermost ringcould be served using F₁, F₂ or FSO. Note that more than two frequencybands may be used by the drone 110 and GTs 120 and the embodimentsdescribed in this disclosure extend to any number of frequency bandsand/or FSO, etc.

In one implementation, rain fade may be mitigated by allocating enoughlink margin in the link budget for the different frequency bands basedon their fading characteristics. In some cases, relying on allocatingadequate link margin to mitigate rain or other atmospheric effects maybe undesirable (e.g., where desired reliability would require excessiveamounts of margin, etc.) Below, additional exemplary techniques aredescribed to reduce the amount of link margin needed to mitigate rainand other atmospheric effects.

In one aspect of this disclosure, the drone 110 and GT radio sub-systems122 measure a signal quality metric, such as SINR (Signal toInterference plus Noise Ratio), from the received messages from GTs(such as GTs 222, 232, and 212 shown in FIG. 1). The data rate from/tothe drone 110 is adjusted according to the measured SINR. If the SINRreceived at a drone 110 or at a GT 120 degrades due to rain fade,resulting in a reduction in the data rate between the drone 110 and theGT 120, then in one exemplary implementation the degradation may beremedied by allocating more time slots or more frequency to the specificaffected GT 120 to compensate for the lower data rate on thecorresponding link. Suppose, for example, that the data rate between thedrone and a specific GT 120 is reduced by a factor of four (4) due torain fade. If four (4) times the number of time slots is allocated tothe impacted GT 120, then the overall throughput the GT 120 experiencesis the same as without any rain fade. In one variant, if more time isallocated to a GT 120 in rain fade, then at least some time is takenfrom other GTs 120. However, if only a small fraction of GTs 120 in thefootprint of a drone 110 are impacted by atmospheric related fade, thentaking time slots from other GTs 120 and allocating more time slots tothe GT 120 in fade will reduce the throughput of the GTs 120 by a verysmall amount. The foregoing exemplary scheme (adjusting the number oftime slots assigned to each GT 120 according to the data rate betweenthe GT 120 and the drone) aims to equalize the throughput betweendifferent GTs 120 which have been assigned the same grade of service interms of throughput. Those of ordinary skill in the related arts, giventhe contents of the present disclosure, will readily appreciate thatsimilar schemes may be implemented based on e.g., frequency, spreadingfactors, etc.

FIG. 4 describes a flow chart of the exemplary scheme used to adjust theamount of time allocated to the link between a GT 120 and a drone 110 inresponse to rain or other atmospheric effects. In step 402, the drone110 or GT radio sub-system 122 measures a signal quality metric (such asSINR) based on the received messages. Common examples of quality metricsmay include without limitation: Received Signal Strength Indication(RSSI), Signal to Noise Ratio (SNR), Bit Error Rate (BER), Packet ErrorRate (PER), Block Error Rate (BLER), etc. In one embodiment, the drone110 or GT radio sub-system 122 monitors a change in the SINR between thereceived messages.

The changes in signal quality metrics may be monitored continuallybetween the received messages and/or at periodic intervals. In oneimplementation, the periodic intervals may be dynamically changed. Theperiodic interval may be based on a current measurements and/or anamount of change between measurements (between messages and/or over atime period). For example, signal quality measurements may be providedat different intervals based on how quickly the signal quality changes.A rapidly fading channel requires faster updates, whereas a relativelystable radio link can provide less frequent updates.

In still other embodiments, the signal quality metrics may be polled orotherwise provided as requested. For example, in certain situations thedrone 110 or GT 120 may be queried, and the resulting collection ofmeasurements may be used for e.g., network optimization, initialdeployment coverage assessment, handover assessment, redundancy coverageassessment, etc.

In step 404, the GT radio sub-system 122 sends the signal quality metricon the uplink to the drone radio sub-system 112. In one embodiment, themeasured signal quality metric may be sent on the uplink on a periodicbasis to the drone radio sub-system 112 or sent when the measured signalquality metric exceeds one or more threshold values. In oneimplementation, the measured signal quality metric comprises themeasured SINR of one or more previously received messages. In anothervariant, the measured signal quality metric comprises a running averageof SINR over multiple received messages.

In other embodiments, the drone radio sub-system 112 sends the signalquality metric on the downlink to the GT radio sub-system 122.Similarly, the measured signal quality metric may be sent on thedownlink on a periodic basis to the GT radio sub-system 122 or sent whenthe measured signal quality metric exceeds one or more threshold values.

In step 406, the drone radio sub-system 112 or GT radio subsystem 122determines the effective performance that the GT 120 or drone 110 willreceive (or can be expected to receive), based on the measured signalquality. Common examples of performance may include e.g., the amount ofdata (e.g., throughput), the delay in data (e.g., latency),retransmission metrics, predicted BER (or PER, BLER), etc. Bydetermining the effective performance, the drone radio sub-system 112 orGT radio subsystem 122 can determine whether the radio link is adverselyimpacted by atmospheric effects.

In some embodiments, the drone radio sub-system 112 or GT radiosubsystem 122 may additionally consider other factors in addition toeffective performance. For example, such factors may include e.g.,historic performance (e.g., based on time of day and/or position), therate of change of performance (e.g., to detect impending fast fading),known network traffic demands (e.g., peak hour demands, etc.)

In step 408, the drone radio sub-system 112 or GT radio subsystem 122determines the amount of additional resources that must be allocated tothe radio link. For example, a drone radio sub-system 112 may mitigateatmospheric effects in order to provide a similar grade of service foran impacted GT 120 as other GTs 120 with the same promised grade ofservice.

Those of ordinary skill in the related arts will readily appreciate that“resources” are broadly used to refer to any physical or virtual elementof limited availability within the network. Common examples of resourcesinclude e.g., time slots, frequency bands, spreading codes, bandwidth,transmission power, etc. In one embodiment, the additional resources areallocated using one or more fairness criterion. In one implementation,fairness criterion refers to the scheme for allocating an amount ofresources to different terminals. One exemplary fairness criterion,referred to as “equal grade of service” scheduling, attempts to providethe same average throughput to all terminals. To achieve equal grade ofservice more time is allocated to terminals that have lower signalquality and/or which receive data at lower data rates. Another exemplaryfairness criterion referred to as “equal grade of time” schedulingallocates the same amount of time to multiple GTs 120. In equal grade oftime scheduling, different GTs 120 will receive different average datathroughputs commensurate with their received signal quality.

In some implementations, the allocation can take effect immediately.Alternatively, in some implementations, an appropriate time for theallocation to take effect must be determined. For example, in someinstances, the radio link between the drone and/or GT is subject tobroader network or usage considerations such as e.g., network traffic,neighboring interference and/or other radio links, etc. Under suchconditions, the drone and/or GT must coordinate the allocation so as toe.g., minimize impact on neighbors, or optimize overall benefits gained.

In step 410, the drone radio sub-system 112 or GT radio subsystem 122changes the scheduler parameters that determine how many resources areallocated to each GT 120. Responsively, the communication between thedrone 110 and each GT 120 is configured in accordance with the scheduledparameters, and thereafter the allocation can take effect. In someembodiments the allocation change may occur at e.g., a prescribedeffective time (e.g., via a time stamp), at a predetermined time (e.g.,at the start of the next cycle, frame, etc.), responsive to a triggerevent (such as signaling), etc.

While the foregoing example is presented with respect to a drone radiosub-system 112 and a GT radio subsystem 122, the concepts describedtherein can be generalized to a network of multiple drones and/or GTs.Moreover, it should be further appreciated by those of ordinary skill inthe related arts given the contents of the present disclosure, thatvarious steps of the method may be performed by other entities; forexample, an evaluation of fairness criterion may be performed by a droneor GT network controller, etc.

Another exemplary method may mitigate atmospheric fade by switching aterminal that is operating at a higher frequency band to a lowerfrequency band. As previously noted, different frequency bands havedifferent susceptibility to atmospheric effects. For example, a terminalusing the higher frequency F₂ that is experiencing excessive rain fadeis configured to switch to a lower frequency band F₁ (or anotherfrequency with more rain fade margin). The GT radio sub-system 122 makesmeasurements of a signal quality metric such as SINR (Signal toInterference plus Noise Ratio) on the received messages from the drone110 and reports the measured SINR or another signal quality to the droneradio sub-system 112. In one implementation, if the measured SINR fallsbelow a certain threshold, then the drone radio sub-system 112 mayinitiate switching the communication link to the second frequency bandF₁ by sending a message configured to inform the GT 120, of the switchto the alternative frequency. Since the second frequency incurs lessrain fade, the link quality will improve by switching to a secondfrequency. Note that the drone radio sub-system 112 may also decide toswitch the operating frequency to a second frequency based on the SINRor another signal quality metric measurement at the drone receiver.Similarly, with regards to FSO which suffers from fog and clouds, thesystem will switch from FSO to a radio frequency mode, F₁ or F₂ when thefade in FSO mode is excessive. This hybrid drone radio sub-systemconstruction allows use of multiple transmission media in order toprovide high throughput, and at the same time optimizes the use of eachmedium according to the rain and other atmospheric conditions. Note thatswitching the GTs 120 to the medium that has the least rain/atmosphericloss at a given time also allows the system to maximize the overallsystem throughput.

FIG. 5 is a flow chart of an exemplary mechanism useful for detectingrain and other atmospheric fades, and to switch the transmission mediumto a second medium. In step 502, the drone radio sub-system 112 or GTradio subsystem 122 measures a signal quality metric, such as SINR. Thesignal quality metric is measured from one or more communicationsbetween the drone and the GT. The measured signal quality metric may bemeasured from one or more particular types of received messages.Alternatively, the signal quality metric may be measured on any messagereceived at a determined periodic interval. The periodic interval may beset as a predetermined time or may be configured to dynamically changebased on one or more parameters. In one such implementation, theperiodic interval is changed based at least in part on the measuredsignal quality metric.

In step 504, the measured signal quality metric is reported to the droneradio sub-system 112 or GT radio subsystem 122. The reported measuredsignal quality metric may comprise a measurement of a particularcommunication itself or may comprise a change in a measured signalquality metric. The GT radio sub-system 122 may be configured to reportthe measured SINR on a periodic basis, reported upon the measured SINRexceed a threshold, or a combination of both. In one implementation, theperiodic basis is configured to dynamically change based at least inpart on the value of the measured and/or reported SINR.

In step 506, the drone radio sub-system 112 or GT radio subsystem 122determines whether the measured signal quality metric is below a certainthreshold indicating excessive fade due to rain, fog, cloud or othereffects. If the measured signal quality metric is below a threshold thenthe drone radio sub-system 112 or GT radio subsystem 122 switches thetransmission medium to an alternate transmission medium (e.g., from F₂to F₁, or from FSO to a radio frequency mode, F₁ or F₂). In someembodiments, the drone radio sub-system 112 or GT radio subsystem 122requests that the transmission medium be switched (causing anothersupervisory entity to responsively perform the switch). For example, thedrone radio subsystem 112 may decide to request a transmission mediumchange based on uplink SINR measurements at the drone receiver.Alternatively, the GT radio subsystem 122 may request a switch of thetransmission medium based on the downlink SINR measurement by sending amessage to the drone 110 with information on the new transmission mediumand the time to switch to the new medium. One exemplary benefit ofhaving the drone 110 decide when to switch transmission medium, as shownin FIG. 5, is that the drone may have information on all traffic andthus may be better suited to schedule GTs 120 on different media, whilebalancing the traffic among different media. It is appreciated however,that in GT initiated embodiments, the GT 120 may have information whichthe drone 110 may not be aware of (e.g., application requirements, etc.)In still other embodiments, a core network entity may manageconnectivity, handovers, etc.

Another aspect of the present disclosure is the use power control tomitigate effects of atmospheric fade on the downlink. In one exemplaryembodiment of the drone radio and transmission medium fixture design,the drone radio sub-system 112 and each antenna aperture for eachfrequency generate multiple beams to different GTs 120. The total powertransmitted by an antenna aperture is configured to be sharable amongthe multiple beams formed toward different GTs 120. The GTs 120 servedby a drone 110 may be located in a wide geographic area where all GTs120 are not simultaneously affected by e.g., rain. When some GTs 120experience atmospheric fade, the drone radio sub-system 112 may allocatemore power to the downlink on the beam toward the affected GT 120. TheGT radio sub-system 122 measures SINR received on the downlink pilotsignals and reports the measured values to the drone 110 in signalingmessages sent to the drone 110 on the uplink. The drone radio sub-system112 determines the amount of rain fade based on the expected SINR valuesin absence of rain. The drone radio sub-system 112 then may increase thepower allocated to the downlink of the affected GTs 120 (i.e., whosereceived SINR have decreased due to rain fade). Note that even in thepower control scheme just described, in one exemplary implementation,certain power margins are allocated in the link budget of the downlinkfrom the drone 110 in order to compensate for rain fade. However, usingpower control and allocating more power only on the downlink beams toGTs 120 in rain fade, the rain fade margin in effect is shared amongdifferent GTs 120, and therefore may result in less link margin beingallocated to rain fade as compared to a scheme where each downlink isallocated its own dedicated rain fade margin. The power control basedrain fade mitigation scheme, therefore, may significantly reduce therequired rain fade margin, thereby resulting in a more efficient system.The above mentioned exemplary power control based rain fade mitigationscheme may increase effectiveness in streaming services where thetraffic mainly flows on the downlink to the terminal.

FIG. 6 is a block diagram of an exemplary modulation and power controlsub-system for the transmitter (TX) unit of FIGS. 2A and 2B. In oneembodiment, the parameters of FIG. 6 are configured such that antennabeams are formed simultaneously toward as many as M terminals using anantenna aperture comprised of N antenna elements. Those of ordinaryskill in the related arts, given the contents of the present disclosure,will readily appreciate that other antenna configurations may be used,the foregoing configuration being purely illustrative. The data for thej-th terminal is encoded using error correction coding block 610-j, andthen mapped onto constellation symbols in block 612-j, as shown forterminals 1 and M. Coded data symbols for the j-th terminal, denoted byS_(j), are scaled by coefficients C_(jk) where k is the index of theantenna element. Coefficients C_(jk) are designed to form beams towardeach terminal. The scaled symbols from different terminals that aredestined to the same antenna element are then summed using the summingdevice 614-k, where k is the index of the summer corresponding to thek-th antenna element. The output of the summer 614-kis then amplifiedand up converted using block 616-k and then sent to antenna element618-k.

FIG. 7 is a flow chart of an exemplary power control based mechanism tomitigate rain fade. In step 702, the GT radio sub-system 122 measuresreceived SINR or some other signal quality metric from the pilot signalson the downlink. In step 704, the GT radio sub-system 122 sends themeasured SINR to the drone radio sub-system 112 in a message on theuplink. In step 706, the drone radio sub-system 112 compares thereceived SINR measurement from the GT 120 against a target SINR. If themeasured SINR is smaller than the target, then in step 708 the droneradio sub-system 112 increases the power on the downlink to thespecified GT 120. If the measured SINR is above the target, then in step710 the drone radio sub-system 112 decreases the power on the downlinkto the specified GT 120.

It will be recognized that while certain aspects of the disclosure aredescribed in terms of a specific sequence of steps of a method, thesedescriptions are only illustrative of the broader methods of thedisclosure, and may be modified as required by the particularapplication. Certain steps may be rendered unnecessary or optional undercertain circumstances. Additionally, certain steps or functionality maybe added to the disclosed embodiments, or the order of performance oftwo or more steps permuted. All such variations are considered to beencompassed within the disclosure disclosed and claimed herein.

While the above detailed description has shown, described, and pointedout novel features of the disclosure as applied to various embodiments,it will be understood that various omissions, substitutions, and changesin the form and details of the device or process illustrated may be madeby those skilled in the art without departing from the disclosure. Thisdescription is in no way meant to be limiting, but rather should betaken as illustrative of the general principles of the disclosure. Thescope of the disclosure should be determined with reference to theclaims.

1. A drone configured to provide broadband access to one or moreterminals, the drone comprising: at least one transmission mediumfixture comprising a plurality of transmission mediums configured toprovide coverage to one or more terminals; wherein various ones of theplurality of transmission mediums are associated with differentresistances to different fading conditions; at least one radiosub-system configured to: demodulate and decode one or more firstsignals received from the one or more terminals; and modulate andtransmit one or more second signals to the one or more terminals; and adrone switching sub-system configured to switch data received at thedrone to another receiving unit of the one or more terminals and/or oneor more drones; wherein the drone switching sub-system is configured toselect a transmission medium based on a measured fading condition. 2.The drone of claim 1, wherein: the one or more terminals comprise one ormore ground-based mobile terminals; the drone radio sub-system isfurther configured to determine an amount of transmission resources tobe allocated to one or more downlinks of the different ones of the oneor more ground-based mobile terminals to equalize a data rate among thedifferent ones of the one or more ground-based mobile terminalsaccording to a fairness criterion; and the drone switching sub-systemfurther comprises a scheduler, the scheduler configured to schedule thedetermined amount of transmission resources to the downlink of thedifferent ones of the one or more ground-based mobile terminals.
 3. Thedrone of claim 2, wherein the drone radio sub-system is furtherconfigured to: determine a change on an uplink signal quality receivedfrom different ones of the one or more ground-based mobile terminals dueto one or more atmospheric conditions; and determine an amount oftransmission resources to be allocated to an uplink of the differentones of the one or more terminals to equalize a data rate among thedifferent ones of the one or more terminals according to at least onefairness criterion; and the scheduler is further configured to: schedulethe determined amount of transmission resources to the uplink of thedifferent ones of the one or more terminals; and inform the differentones of the one or more terminals of respective scheduled transmissionresources. 4.-5. (canceled)
 6. The drone of claim 1, wherein the droneradio sub-system is further configured to: determine a change in anamount of power allocated on a downlink to at least one of the one ormore terminals to equalize the data rate among different terminalsaccording to at least one fairness criterion; and adjust the powerallocated to the downlink of to one or more of the one or moreterminals.
 7. The drone of claim 6, wherein the drone radio sub-systemis further configured to: encode terminal data; map the coded bits ontoconstellation symbols; scale the coded symbols from each terminaldestined to different antenna elements to form a beam toward arespective terminal; sum the scaled coded symbols for differentterminals destined to a same antenna aperture to form multiple beams,one toward each respective terminal; modulate the resulting symbols ontothe selected transmission medium and transmit the resulting signalthrough the corresponding antenna aperture.
 8. The drone of claim 7,wherein the drone radio subsystem is further configured to choose thescale for coded symbols for each terminal to adjust the power sent to aterminal on the respective downlink.
 9. A method of providing broadbandaccess using a plurality of drones, the method comprising: measuring asignal quality metric for one or more terminals of a plurality ofterminals; comparing the measured signal quality metric versus one ormore threshold values; determining if the signal quality metric of theone or more terminals has degraded due to one or more atmosphericconditions; and select a different transmission medium when the signalquality metric of the one or more terminals has degraded.
 10. The methodof claim 9, further comprising: determining a number of transmissionresources that an uplink and downlink to the one or more terminal needsin order to equalize the throughput to different ones of the pluralityof terminals according to a specified fairness criterion; informing ascheduler of the allocated number of transmission resources for aterminal link of the one or more terminals; and sending a message to oneor more terminals comprising respective uplink transmission resourceallocations.
 11. The method of claim 9, further comprising switching toa second transmission medium to mitigate atmospheric-related fading. 12.The method of claim 9 further comprising adjusting a power allocated toeach terminal on a downlink according to a change in the measured signalquality metric.
 13. A mobile terminal, comprising: a mobile terminalradio sub-system comprising at least one transmission medium fixtureconfigured to receive data signaling on at least two transmissionmediums having different resistance to atmospheric effects, the mobileterminal radio sub-system configured to: demodulate and decode one ormore first signals received on at least one transmission medium of theat least two transmission mediums from at least one of one or moredrones; responsive to a switch instruction, the at least onetransmission medium fixture switches to a different transmission mediumof the at least two transmission mediums.
 14. The mobile terminal ofclaim 13, wherein the mobile terminal radio sub-system is furtherconfigured to: measure a received downlink signal quality to determine asignal quality change due to atmospheric conditions; and send themeasured signal quality to the at least one radio sub-system of the oneor more drones.
 15. The mobile terminal of claim 13, wherein the mobileterminal radio sub-system is further configured to measure a change in areceived downlink signal quality to determine a signal quality changedue to one or more atmospheric conditions; and send the measured changein a received downlink signal quality to the drone radio sub-system. 16.The mobile terminal of claim 13, wherein the mobile terminal radiosub-system is further configured to: measure a received downlink signalquality to determine a change in signal quality due to one or moreatmospheric conditions; and send the measured signal quality to at leastone drone.
 17. The mobile terminal of claim 13, wherein the one or moreatmospheric conditions are selected from the group consisting of: (i)fog, (ii) clouds, and (iii) rain.
 18. (canceled)
 19. The mobile terminalof claim 13, wherein the mobile terminal radio sub-system is furtherconfigured to: receive a schedule of transmission resources to use forcommunication with at least one drone; and configure communication tothe at least one drone based on the received schedule.
 20. The mobileterminal of claim 13, wherein the measured signal quality comprises asignal to interference plus noise ratio (SINR).